<html>
	<head>
		<script language="javascript">
			
			function dataValidator(){
				var radio = document.getElementById("radio")
				
				var datos = document.getElementById("datos")
				
				var ok = true;
				
				if(isNaN(radio.value) || radio.value == ""){
					ok = false
				}
				if(ok){
					datos.submit();
				}
			}
			
		</script>
	</head>
	<body>
		<form method="POST" action="calcula_area.php?figura=circulo" id="datos" name="datos">
			<table>
				<tr>
					<td class="req">Radio:</td><td><input type="text" id="radio" name="radio"/></td>
				</tr>				
				<tr><td colspan=2 align="center"><input type="button" value="Calcular" onClick="dataValidator()" ></td></tr>				
			</table>	
		
		</form>
	</body>
</html>